It is known to provide heavy construction-type equipment at each of its wheels with a so-called wheel drive. Such a drive usually has a hydraulic motor and a transmission, normally of the planetary-gear type, connected between the wheel and the frame. Each wheel has such a drive for maximum maneuverability and to eliminate a lengthy drive shaft, which normally cannot be accommodated on such a vehicle.
Such wheel drives are extremely effective at low speeds, and indeed give excellent traction as all wheels are powered. At high speeds, however, it is standard parctice to employ only the wheel drives of the front or rear wheels. The full output of the pump of the machine is fed only to the two drives that are used. During such high-speed operation the nondriving wheel drives are, however, still driven pump-fashion by their respective wheels. In order to minimize friction the intakes and outputs of these drives are connected together so that the motors present little resistance to rotation.
Such an arrangement has been found unsatisfactory. First of all even though the intakes and outputs are connected together, the motors do normally present some drag on the wheels, so that energy is wasted. At the same time the motors are operated at high speed and often are subjected to excessive wear during such operation, when in fact the motors are doing no useful work. As a result the service life of such a wheel drive is correspondingly reduced.